The present invention relates to a method for the production of antistatic films of synthetic polymers, to the products obtained by this method, and to some applications of the products.
It is known that synthetic polymers, owing to their non-conductivity, readily acquire but do not easily lose static electrical charges. The generation of static electricity onto the surface of plastic materials may occur in several ways during the period extending from their production to their final use. One way is through the friction caused by extrusion or even through pulling a film over the rollers of a packaging machine.
Static electricity has detrimental effects in various applications of synthetic polymers. In the packaging industry, first it causes the attraction of dust which ruins the clarity of a polymer film, secondly, it causes handling problems which result from the polymers adhering to metal parts of the packaging machine, and thirdly it causes electrical discharges which may start a fire and/or explosion.
Previously, two means have been proposed for resolving these problems. The first means is the use of air-ionizing bars which provide negative and positive ions that neutralize the plastic. This is an effective means of reducing fire and explosion hazards, but provides only temporary protection. The second means is the incorporation into the synthetic polymer of antistatic chemical agents such as quaternary ammonium compounds, phoshate esters, and polyglycol esters of fatty acids which are hygroscopic and remain on the polymer surface. Nevertheless, depending on the method of incorporation used, they have the disadvantage of being easily removed from the plastic surface by handling or cleaning or of only producing their effect for several days or several weeks after incorporation. On the other hand, when used for packaging food, there is a danger of their coming into contact with the food, making it unsuitable for consumption, and their presence reduces some polymer properties such as heat sealibility and printability. Furthermore, surface resistivity of polymers comprising such agents cannot be reduced below 10.sup.10 ohms/cm, whereas surface resistivity of unmodified polymers is about 10.sup.16 to 10.sup.18 ohms/cm.